Honor the expected behavior of syncfs() to synchronously flush all data
and metadata on linux systems.
If virtiofsd is started with '-o announce_submounts', the client is
expected to send a FUSE_SYNCFS request for each individual submount.
In this case, we just create a new file descriptor on the submount
inode with lo_inode_open(), call syncfs() on it and close it. The
intermediary file is needed because O_PATH descriptors aren't
backed by an actual file and syncfs() would fail with EBADF.
If virtiofsd is started without '-o announce_submounts', the client
only sends a single FUSE_SYNCFS request, for the root inode. In this
case, we need to loop on all known submounts to sync them. We cannot
call syncfs() with the lo->mutex held since it could stall virtiofsd
for an unbounded time : let's generate the list of inodes with the
mutex held, drop the mutex and then loop on the temporary list. A
reference must be taken on each inode to ensure it doesn't go away
when the mutex is dropped.
Note that syncfs() might suffer from a time penalty if the submounts
are being hammered by some unrelated workload on the host. The only
solution to prevent that is to avoid shared mounts.
Signed-off-by: Greg Kurz <gr...@kaod.org>
---
tools/virtiofsd/fuse_lowlevel.c | 11 +++
tools/virtiofsd/fuse_lowlevel.h | 13 ++++
tools/virtiofsd/passthrough_ll.c | 98 +++++++++++++++++++++++++++
tools/virtiofsd/passthrough_seccomp.c | 1 +
4 files changed, 123 insertions(+)
diff --git a/tools/virtiofsd/fuse_lowlevel.c b/tools/virtiofsd/fuse_lowlevel.c
index e4679c73abc2..e02d8b25a5f6 100644
--- a/tools/virtiofsd/fuse_lowlevel.c
+++ b/tools/virtiofsd/fuse_lowlevel.c
@@ -1876,6 +1876,16 @@ static void do_lseek(fuse_req_t req, fuse_ino_t nodeid,
}
}
+static void do_syncfs(fuse_req_t req, fuse_ino_t nodeid,
+ struct fuse_mbuf_iter *iter)
+{
+ if (req->se->op.syncfs) {
+ req->se->op.syncfs(req, nodeid);
+ } else {
+ fuse_reply_err(req, ENOSYS);
+ }
+}
+
static void do_init(fuse_req_t req, fuse_ino_t nodeid,
struct fuse_mbuf_iter *iter)
{
@@ -2280,6 +2290,7 @@ static struct {
[FUSE_RENAME2] = { do_rename2, "RENAME2" },
[FUSE_COPY_FILE_RANGE] = { do_copy_file_range, "COPY_FILE_RANGE" },
[FUSE_LSEEK] = { do_lseek, "LSEEK" },
+ [FUSE_SYNCFS] = { do_syncfs, "SYNCFS" },
};
#define FUSE_MAXOP (sizeof(fuse_ll_ops) / sizeof(fuse_ll_ops[0]))
diff --git a/tools/virtiofsd/fuse_lowlevel.h b/tools/virtiofsd/fuse_lowlevel.h
index c55c0ca2fc1c..b889dae4de0e 100644
--- a/tools/virtiofsd/fuse_lowlevel.h
+++ b/tools/virtiofsd/fuse_lowlevel.h
@@ -1226,6 +1226,19 @@ struct fuse_lowlevel_ops {
*/
void (*lseek)(fuse_req_t req, fuse_ino_t ino, off_t off, int whence,
struct fuse_file_info *fi);
+
+ /**
+ * Synchronize file system content
+ *
+ * If this request is answered with an error code of ENOSYS,
+ * this is treated as success and future calls to syncfs() will
+ * succeed automatically without being sent to the filesystem
+ * process.
+ *
+ * @param req request handle
+ * @param ino the inode number
+ */
+ void (*syncfs)(fuse_req_t req, fuse_ino_t ino);
};
/**
diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index 7bf31fc129c8..9021eb091a28 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -3362,6 +3362,103 @@ static void lo_lseek(fuse_req_t req, fuse_ino_t ino,
off_t off, int whence,
}
}
+static int do_syncfs(struct lo_data *lo, struct lo_inode *inode)
+{
+ int fd, err = 0;
+
+ fuse_log(FUSE_LOG_DEBUG, "lo_syncfs(ino=%" PRIu64 ")\n", inode->fuse_ino);
+
+ fd = lo_inode_open(lo, inode, O_RDONLY);
+ if (fd < 0) {
+ return -fd;
+ }
+
+ if (syncfs(fd) < 0) {
+ err = -errno;
+ }
+
+ close(fd);
+ return err;
+}
+
+struct syncfs_func_data {
+ struct lo_data *lo;
+ int err;
+};
+
+static void syncfs_func(gpointer data, gpointer user_data)
+{
+ struct syncfs_func_data *sfdata = user_data;
+ struct lo_data *lo = sfdata->lo;
+ struct lo_inode *inode = data;
+
+ if (!sfdata->err) {
+ sfdata->err = do_syncfs(lo, inode);
+ }
+
+ lo_inode_put(lo, &inode);
+}
+
+static int lo_syncfs_all(fuse_req_t req)
+{
+ struct lo_data *lo = lo_data(req);
+ GHashTableIter iter;
+ gpointer key, value;
+ GSList *list = NULL;
+ struct syncfs_func_data sfdata = {
+ .lo = lo,
+ .err = 0,
+ };
+
+ pthread_mutex_lock(&lo->mutex);
+
+ g_hash_table_iter_init(&iter, lo->mnt_inodes);
+ while (g_hash_table_iter_next(&iter, &key, &value)) {
+ struct lo_inode *inode = value;
+
+ /* Reference is put in syncfs_func() */
+ g_atomic_int_inc(&inode->refcount);
+ list = g_slist_prepend(list, inode);
+ }
+
+ pthread_mutex_unlock(&lo->mutex);
+
+ g_slist_foreach(list, syncfs_func, &sfdata);
+ g_slist_free(list);
+ return sfdata.err;
+}
+
+static int lo_syncfs_one(fuse_req_t req, fuse_ino_t ino)
+{
+ struct lo_data *lo = lo_data(req);
+ struct lo_inode *inode;
+ int err;
+
+ inode = lo_inode(req, ino);
+ if (!inode) {
+ return -EBADF;
+ }
+
+ err = do_syncfs(lo, inode);
+ lo_inode_put(lo, &inode);
+ return err;
+}
+
+static void lo_syncfs(fuse_req_t req, fuse_ino_t ino)
+{
+ struct lo_data *lo = lo_data(req);
+ int err;
+
+ if (lo->announce_submounts) {
+ err = lo_syncfs_one(req, ino);
+ } else {
+ err = lo_syncfs_all(req);
+ }
+
+ fuse_reply_err(req, err);
+}
+
+
static void lo_destroy(void *userdata)
{
struct lo_data *lo = (struct lo_data *)userdata;
@@ -3423,6 +3520,7 @@ static struct fuse_lowlevel_ops lo_oper = {
.copy_file_range = lo_copy_file_range,
#endif
.lseek = lo_lseek,
+ .syncfs = lo_syncfs,
.destroy = lo_destroy,
};
diff --git a/tools/virtiofsd/passthrough_seccomp.c
b/tools/virtiofsd/passthrough_seccomp.c
index a3ce9f898d2d..3e9d6181dc69 100644
--- a/tools/virtiofsd/passthrough_seccomp.c
+++ b/tools/virtiofsd/passthrough_seccomp.c
@@ -108,6 +108,7 @@ static const int syscall_allowlist[] = {
SCMP_SYS(set_robust_list),
SCMP_SYS(setxattr),
SCMP_SYS(symlinkat),
+ SCMP_SYS(syncfs),
SCMP_SYS(time), /* Rarely needed, except on static builds */
SCMP_SYS(tgkill),
SCMP_SYS(unlinkat),
--
2.34.1
